Magic Hour

Replace character in video

replace_character_in_video

Use only with the user's own likeness or content they are authorized to use. Do not use for impersonation, deception, sexual content, or content involving minors.

Replaces a subject in a video with a character from a reference image, or transfers the video's motion onto that character. Starts a background job that costs credits; returns a project id for wait_for_video_project.

Input Schema

Name	Required	Description	Default
`name`	No	Give your video a custom name for easy identification.	Character Replace - dateTime
`model`	No	Model to use. Defaults to `wan-animate`. * `wan-animate`: 480p, 720p. Supports `points` subject selection. * `kling-3.0`: 720p, 1080p. Clips of 3–10 seconds in `replace` mode or 3–30 seconds in `animate` mode. Picks the main person automatically, so `points` are rejected. * `minimax-h3`: 480p, 720p, 1080p. Clips of 1–60 seconds in `replace` mode or 1–60 seconds in `animate` mode. Subject `points` are `replace`-only; `animate` with `selection_mode` `point` returns 422, and with `auto` or no `selection_mode` the points are ignored.	wan-animate
`style`	No	Optional style controls for replace vs animate mode and subject selection.
`assets`	Yes	Source video and reference character image for the job.
`resolution`	No	Output video resolution. Must be supported by `model`. Defaults to the lowest resolution available on your plan for that model.
`end_seconds`	Yes	End time of your clip (seconds). Must be greater than start_seconds.
`start_seconds`	No	Start time of your clip (seconds). Must be ≥ 0.

Output Schema

Name	Required	Description	Default
`id`	Yes	Unique ID of the video. Use it with the [Get video Project API](https://docs.magichour.ai/api-reference/video-projects/get-video-details) to fetch status and downloads.
`credits_charged`	Yes	The amount of credits deducted from your account to generate the video. If the status is not 'complete', this value is an estimate and may be adjusted upon completion based on the actual FPS of the output video. If video generation fails, credits will be refunded, and this field will be updated to include the refund.

Schema Changelog

Changes observed during successful MCP inspections.

AddedOct 30, 2026

TDQS

A3.9/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Beyond the annotations (readOnly=false, destructive=false, openWorld=true), the description discloses that this is an asynchronous background job, that it consumes credits, and that it returns a project id to poll with wait_for_video_project. That is meaningful context the annotations do not carry; it only lacks detail on failure/validation behavior.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Three sentences, no filler, and the mechanical workflow statement is tight. The safety policy leads the description, which slightly defers the core 'what it does' statement rather than front-loading it, but nothing is wasted.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a 7-param, nested-schema, credit-consuming async tool with an output schema available, the description covers purpose, safety constraints, and the follow-up polling step. Model/point compatibility rules live in the schema and need not be repeated; only alternative-tool routing is absent.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the schema already documents all 7 parameters, including the model-specific replace/animate constraints. The description adds no parameter-level detail beyond what the schema provides, so the baseline 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb+resource ('Replaces a subject in a video with a character from a reference image') and describes the alternative 'animate' mode (motion transfer). It does not name the closest siblings (swap_face_in_video, place_person_in_scene, restyle_video), so the agent must infer differentiation from the mode wording alone.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives explicit when-not guidance via the policy sentence (only own likeness/authorized content; no impersonation, deception, sexual content, minors) and tells the caller what happens next (background job, credits, project id for wait_for_video_project). It stops short of routing to competing tools when the user wants just a face swap or a static scene placement.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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